Effects of gripping volume in the mechanical strengths of orthodontic mini-implant

The objective of study was to investigate the correlation between the mechanical strengths [insertion torque (IT); resonance frequency (RF); and horizontal pullout strength (HPS)] and gripping volume (GV) of mini-implants. Thirty mini-implants of three types (Type A: 2 mm × 10 mm, cylindrical, titanium alloy; Type B: 2 mm × 10 mm, tapered, stainless steel; and Type C: 2 mm × 11 mm, cylindrical, titanium alloy) were inserted 7 mm into artificial bones. One-way analysis of variance and Spearman's test were applied to assess intergroup comparisons and intragroup correlations. The null hypothesis was that no statistically significant correlations exist between the GV and mechanical strengths (IT, RF, and HPS). In the IT test, Type C (14.2 Ncm) had significantly (p = 0.016) greater values than did Type A (12.4 Ncm). In the RF analysis, no significant difference was observed among the three types of mini-implants. In the HPS test, Type C (388.9 Ncm) was significantly larger than both Type B (294.5 Ncm) and Type A (286 Ncm). In the GV measurement, Type C (14.4 mm³) was significantly larger than Type B (11.4 mm³) and Type A (9.2 mm³). Type A and Type B exhibited no significant correlations among the tests. Therefore, the null hypothesis was accepted. Although no significant correlation was noted between the GV and mechanical strengths (IT, RF, and HPS), we observed a trend that the mechanical strengths (IT, RF, and HPS) of the mini-implants corresponded to the order and values of GV (Type C > Type B > Type A).     

Evaluation of the wash resistance of three types of manufactured insecticidal nets in comparison to conventionally treated nets

The present study evaluated the efficacy and wash resistance of several commercial deltamethrin-treated nets (PermaNet™, from factory (PN-F) and market (PN-M), Yorkool (Y) and AZ net) that were claimed by the manufacturers to be Long-Lasting Insecticide Treated Nets (LLITNs), compared to ITNs conventionally treated with deltamethrin (23-27 mg/m², using one K-O Tab^® tablet (KO) per net). Montpellier washing technique was used for washing the pieces of the nets. Insecticidal activity was assessed on dried pieces of nets after 0, 2, 5, 8, 11, 15, 18 and 21 washes, using two types of bioassay (mean median knock down times and mortality 24 h after a 3-min exposure) and reared female Anopheles stephensi. To evaluate the effect of heat on diffusion of insecticide from inside of the nets to the surface of them, some Permanet nets were heated. For all the types of nets tested the median knock down time (MKDT) increased approximately linearly with number of washes. The slopes of the lines (increase of MKDT per wash) were low with the PN-F and PN-M, intermediate with Y and equally high with KO and AZ. No significant differences can be claimed with the 3-min exposure tests. The slopes of the regression lines did not differ significantly between the heated and unheated samples. It is concluded that diffusion at ambient temperature is fast enough to rapidly compensate for the loss of insecticide on the surface with no need to artificially stimulate diffusion by heating.